/Engine/Source/Runtime/MeshDescription/Public/MeshDescription.h
Deletes polygons from the mesh and remove all orphaned polygon groups, vertex instances, edges and vertices. Will not compact the internal arrays, you must callCompact()manually.
void DeletePolygons ( const [TArray](API\Runtime\Core\Containers\TArray)< [FPolygonID](API\Runtime\MeshDescription\FPolygonID) > & Polygons )